The present invention relates to a device for closing off a liquid-supply channel with an axially moving diaphragm, one face of which demarcates a control space that is located in a lid and that can be connected either to the atmosphere or to a source of vacuum through a control valve and the other face of which demarcates a product space that is also vacuumized and that accommodates the liquid-supply channel, such that the diaphragm can, in one of its limiting positions, close the opening of the channel.
A device of this type is known from GB Patent 2 064 823 and can be employed in milking systems etc. The purpose of the device is to close off the liquid-supply channel in the product space when the pressure therein rises. The diaphragm accordingly activates a piston that is maintained in position by vacuum. Since a specific level of force is necessary to do so, the action cannot be initiated until the pressure in the product space has increased enough to be applied by the diaphragm. The device is relatively expensive to manufacture.